In this post I will show you how to get the parent URL of a child product EFFICIENTLY (that means, unlike the very common mistake most Magento developers do, it is a way that will not slow your website down).

Let's say you have configurable products in your Magento site.
Each configurable product has 1 parent product (configurable product) and some (let's say 2) children (simple product). Let's say you wish to display the product list on your category page, but each product should have it's parent URL.

Lets implement this:
I assume you wish to implement this in base/default/template/catalog/product/list.phtml

<?php $i=0; foreach ($_productCollection as $_product):
	$prodId = $_product->getId();
	$arrayOfParentIds = Mage::getSingleton("catalog/product_type_configurable")
        ->getParentIdsByChild($prodId);
	$parentId = (count($arrayOfParentIds) > 0 ? $arrayOfParentIds[0] : null);
	$url = $_product->getProductUrl();
	if(!is_null($parentId)){
		$url = Mage::getModel("catalog/product")->load($parentId)->getProductUrl();
	}
?>

This implementation will work, but it isn't recommended when performing on a large collection (more than 5 products / page). why? Because, the action

Mage::getModel("catalog/product")->load($parentId);

is pretty expensive in terms of efficiency (in other words - it takes large amount of time for the server to perform this action). looping on this action more than once or twice will slow your website down dramatically.

So here is the alternative. might be more complicated, but a lot more efficient (implementation):

<?php
        $rewrite = Mage::getModel('core/url_rewrite');

	$params = array();
	$params['_current']     = false;

	?>
	<?php $i=0; foreach ($_productCollection as $_product):

	$prodId = $_product->getId();
	$arrayOfParentIds = Mage::getSingleton("catalog/product_type_configurable")
        ->getParentIdsByChild($prodId);
	$parentId = (count($arrayOfParentIds) > 0 ? $arrayOfParentIds[0] : null);
	$url = $_product->getProductUrl();
	$idPath = 'product/'.$parentId;
	$rewrite->loadByIdPath($idPath);

	$parentUrl = Mage::getUrl($rewrite->getRequestPath(), $params);
	$url = ($parentUrl ? $parentUrl : $url);
	?>

This implemenation is much more cheaper in terms of efficiency, because we use

$rewrite->loadByIdPath($idPath);

instead of the expensive

Mage::getModel("catalog/product")->load($parentId);

which means, less loading time.

That's all :-)

On this part, we will make the text "Hello World" appear inside the Magento design.

For this, go to app/code/local/Engineering/Helloworld/controllers/IndexController.php and change its code to following:

<?php class Engineering_Helloworld_IndexController extends Mage_Core_Controller_Front_Action
{
	public function indexAction()
	{
	    $this->loadLayout();
            $this->renderLayout();
	}
}

A short explanation:
When calling to

$this->loadLayout();

Magento will go to "app/design/myinterface/mytheme/layout" (on a fresh Magento installation, it actually "app/design/base/default/layout") reads all the XML files and searches there for a tag named layout and loads the found data to "core/layout" object.
Now, when calling to

$this->renderLayout();

the layout will be rendered.

Now lets go to www.mysite.com/helloworld - we will see some empty standard Magento design. It's because only tags get loaded.

Now go to app/code/local/Engineering/Helloworld/etc/config.xml and add some change to it:

<?xml version="1.0"?>
<config>
 <modules>
  <Engineering_Helloworld>
   <version>0.1.0</version>
  </Engineering_Helloworld>
 </modules>
 <frontend>
  <routers>
   <engineering_helloworld>
    <use>standard</use>
    <args>
     <module>Engineering_Helloworld</module>
     <frontName>helloworld</frontName>
    </args>
   </engineering_helloworld>
  </routers>
  <layout>
   <updates>
    <engineering_helloworld>
     <file>helloworld.xml</file>
    </engineering_helloworld>
  </updates>
  </layout>
 </frontend>
</config>

This tells magento to regard the file named helloworld.xml as another layout file. Now create the helloworld.xml at:
app/design/frontend/default/default/layout/helloworld.xml
Type in the following:

<?xml version="1.0"?>
<layout version="0.1.0">
 <engineering_helloworld_index_index>
  <reference name="content">
   <block type="core/template" name="helloworld.text"
   template="engineering/helloworld/sayhello.phtml"/>
  </reference>
 </engineering_helloworld_index_index>
</layout>

Because the URL is www.mysite.com/helloworld/index/index magento will load the content of <helloworld_index_index> tag to the layout object.  Afterwards, the

$this->renderLayout();

will put the block named "helloworld.text" to the block named "content",  load the block class "core/template" (Mage_Core_Block_Template) and template "engineering/helloworld/sayhello.phtml" (app/design/frontend/myinterface/mytheme/engineering/helloworld/sayhello.phtml)  for this block.

Now, create "sayhello.phtml" at
app/design/frontend/default/default/template/engineering/helloworld/sayhello.phtml
type there just

Hello World

Now, go to www.mysite.com/admin/helloworld - you should see the text "Hello world" inside magento design.

In this tutorial we will create a Magento extension step by step. our extension will print "Hello World" to the screen.

Go to "app/code/local" and create a new folder. name it "Packagename" - the "Packagename" is likely to be your company name - this folder will serve all the extensions that will be made by your company. I'll call it "Engineering".

Inside the "Packagename" folder, create another folder named "Modulename" - the "Modulename" is the name of your module - I'll name it "Helloworld". now we should have the following path:

app/code/local/Engineering/Helloworld

Now you have to tell Magento about your extension, so create a file named "Engineering_Helloworld.xml" in the following path:

app/etc/modules/Engineering_Helloworld.xml

type in the following:

<?xml version="1.0"?>
<config>
  <modules>
   <Engineering_Helloworld>
    <active>true</active>
    <codePool>local</codePool>
   </Engineering_Helloworld>
  </modules>
</config>

Magento is a configuration-set MVC system. that means, if you want the URL

www.mysite.com/helloworld/index/index

will display "Hello World", you need to tell Magento about this. Create a file named "config.xml" in the following path (create the etc folder, also):

app/code/local/Engineering/Helloworld/etc/config.xml

type in the following:

<?xml version="1.0"?>
<config>
 <modules>
  <Engineering_Helloworld>
   <version>0.1.0</version>
  </Engineering_Helloworld>
 </modules>
 <frontend>
  <routers>
   <engineering_helloworld>
    <use>standard</use>
    <args>
     <module>Engineering_Helloworld</module>
     <frontName>helloworld</frontName>
    </args>
   </engineering_helloworld>
  </routers>
 </frontend>
</config>

A short explanation about the config.xml tags:
The <use> tag in the <router> hierarcy, tells Magento whether the <router> tag refers to admin url or the frontend url. we want the URL www.mysite.com/helloworld/index/index, and not  www.mysite.com/admin/helloworld/index/index, so that means we need the frontend. the <use> is "standard" (other options are "admin" and "default").
The tag <engineering_helloworld> under <routers> seems to be arbitrary, but sure, there are conventions, so you need to write your full module name in lower case.
The tag <frontName> tells Magento about the first string of your extension's URL, so the URL is:
www.mysite.com/helloworld/index/index
and not, for example
www.mysite.com/byeworld/index/index
[Note: you have to make sure that the term "helloworld" isn't already occupied by other extension or core module, otherwise the Magento's behavior will be unpredicted.]

Now it's time to write the code for the output "Hello World":
For us, to make the page

www.mysite.com/helloworld/index/index

display "Hello World", we need to create a file named "indexController.php" at:

app/code/local/Engineering/Helloworld/controllers/IndexController.php

and type in the following code:

<?php
class Engineering_Helloworld_IndexController extends Mage_Core_Controller_Front_Action
{
    public function indexAction()
    {
    echo "Hello World";
    }
}

Now, go to www.mysite.com/helloworld/index/index, and you should see the desired "Hello World".
So, actually, when you go to www.mysite.com/helloworld/index/index, Magento is looking for a front name "helloworld" through all the active module configurations. if found, it searches for indexController. if found, it's looking for
indexAction inside that controller.
Now try to go to www.mysite.com/helloworld - you should see the same result, this is only because when nothing mentioned after the module name, Magento looking for index/index by default.

On the next post, we will add some design to our extension page - so don't go anywhere :-)

Writing Magento Extension – part2